When it comes to whistles, I don't particularly care if they are compact or not as the size of most whistles is small enough already.

I favor the Fox 40 whistles as I get them for free (courtesy of our local .gov) and also hand them out to others. I always carry two whistles when I am out. One around the neck on a lanyard and the second whistle is in the psk or pack as a backup.
_________________________
Earth and sky, woods and fields, lakes and rivers, the mountain and the sea, are excellent schoolmasters, and teach some of us more than we can ever learn from books.

John Lubbock